Inductor For Inductively Heating A Rotating Workpiece

Abstract

An improvement in a single shot inductor of the type used in heating the total length of an axle shaft as the shaft is rotating about its central axis. The normal single shot inductor includes two generally parallel conductors extending along the length of the shaft and terminating in cross-over conductors at each end with one of the parallel conductors including a gap for accommodating input leads connected to an alternating current source. This basic inductor is improved by providing a conductor loop including at least one auxiliary conductor extending along the outer surface of the shaft between a first position adjacent one of the cross-over conductors and a second position adjacent the other cross-over conductor, with the auxiliary conductor being magnetically coupled to the surface. The conductor loop is connected in electrical series with one of the input leads of the normal single shot inductor so that the current flow within the auxiliary conductor provides an additional heating area in the rotating shaft.

Description

This invention relates to the art of induction heating and more particularly to an improved inductor for inductively heating an elongated rotating workpiece.

The invention is particularly applicable for inductively heating a flanged axle shaft preparatory to quench hardening, and it will be described with particular reference thereto; however, it must be appreciated that the invention has broader applications and may be used in various installations wherein the standard single shot inductor is used to inductively heat the total length of an elongated, generally cylindrical workpiece.

In hardening the outer surface of an axle shaft, it is now becoming somewhat common practice to use a stationary inductor, known as a "single shot" inductor. This single shot inductor includes two generally parallel conductors extending the total length of the cylindrical portion of a shaft and connected at each end by cross-over conductors generally in the form of arcuate conductors extending between the parallel conductors. One of the conductors is provided with a gap to accommodate input leads for directing an alternating current through a loop formed by parallel conductors and the cross-over conductors to heat inductively the shaft portion of the axle shaft as it is rotated about its central axis. When the axle shaft includes a flange, one of the cross-over conductors is positioned adjacent the fillet area between the flange and the elongated cylindrical shaft portion to provide heating in the fillet area of the flanged shaft. After the rotating axle shaft has been heated to a quench hardening temperature, the heating operation is discontinued and the shaft is quench hardened. This procedure for inductively heating the surface of an axle shaft has been quite successful; however, certain difficulties have been experienced. To provide sufficient heating in a relatively short period of time high power densities are necessary. As the power is switched on and off, the inductor flexes primarily at the joint between the parallel conductors and the cross-over conductors. This repeated flexing can cause fatigue cracks in the inductor. Since the inductor includes internal coolant passages, in accordance with normal practice, these fatigue cracks cause leakage of the coolant and require replacement of the inductor when they develop. Many attempts have been made to prevent the premature failure of single shot inductors. For instance, reinforcing of the inductor has been used. This does increase the life of the inductor; however, such reinforcing is relatively expensive and requires substantial man hours to accomplish. Other attempts have included reducing power density of the inductor. This increases the heating time which is not satisfactory because it adds to the cost of the heating operation.

The present invention is directed toward an improved single shot inductor which increases the life and efficiency of the inductor.

In accordance with the present invention, the standard single shot inductor is modified to include a conductor loop including at least one auxiliary conductor extending along the shaft surface of the axle shaft and between a first position adjacent one cross-over conductor and a second position adjacent the other cross-over conductor. The auxiliary conductor is magnetically coupled to the shaft surface and there are provided means for connecting the conductor loop in electrical series with one of the input leads so that the auxiliary conductor is additive in its heating effect.

By using the present invention, a reduced current can be directed through the inductor and still develop the necessary heating of the workpiece surfaces in a relatively short time.

In accordance with another aspect of the present invention, the auxiliary conductor is adjacent one of the parallel conductors and there is means for causing the current flow in the auxiliary conductor to be in phase with the current flow in the adjacent parallel conductor. In this manner, the two conductors create fields which are additive in their heating effect.

The primary object of the present invention is the provision of an improved single shot inductor of the type defined above, which inductor includes a separate conductor loop having at least one conductor adjacent the surface thereof to increase the heating effect by the inductor and thus reduce the required flux densities of the inductor.

Yet another object of the present invention is the provision of an improved single shot inductor of the type defined above, which inductor requires a reduced flux density and, thus, increases the life of the inductor.

Yet another object of the present invention is the provision of an improved single shot inductor of the type defined above, which inductor has a longer life during operation and a higher heating efficiency than prior single shot inductors for the same workpiece.

These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings in which:

FIG. 1 is a pictorial view illustrating the preferred embodiment of the present invention;

FIG. 2 is a top elevational view of the preferred embodiment shown in FIG. 1;

FIG. 3 is a side elevational view, partially in cross-section, showing the preferred embodiment of the present invention as illustrated in FIG. 1;

FIG. 4 is an enlarged cross-sectional view taken generally along line 4--4 of FIG. 3;

FIG. 5 is an enlarged cross-sectional view taken generally along line 5--5 of FIG. 3; and,

FIG. 6 is an enlarged cross-ectional view taken generally along line 6--6 of FIG. 3.

Referring now to the drawings wherein the showings are for the purpose of illustrating the preferred embodiments of the invention only, and not for the purpose of limiting same, FIGS. 1-3 show an induction heating installation A for inductively heating the outer generally cylindrical surface of an elongated workpiece, such as axle shaft B, by an inductor C. The workpiece includes a cylindrical body portion 10 having an outer cylindrical surface, a flange 12 connected onto the body portion 10 by a fillet 14. In accordance with normal practice, there is provided means for rotating the workpiece B about its central axis a. Various arrangements can be used for rotating the workpiece; however, in accordance with the illustrated embodiment of the invention, a rotating motor 20 rotates the workpiece as it is supported between normal centers 22, 24.

The inductor C includes two generally parallel conductors 30, 32 extending substantially the total length of body portion 10 and terminating in axially spaced cross-over conductors 34, 36 which are generally concentric with the surface of portion 10 and spaced therefrom in accordance with the induction heating practice. The inductor C is considered to be a single inductor; however, as is well known in the induction heating art, this inductor includes a gap 40 to define spaced input leads 42, 44. Of course, the input gap can be provided in any of the conductors 30, 32, 34, and 36. As so far explained, inductor C does not differ from the normal single shot inductor used for inductively heating axle shafts preparatory to quench hardening. The cross-over conductor 34 is adjacent fillet 14 for the purpose of heating the fillet portion and a part of the flange for subsequent quench hardening.

In accordance with the present invention, there is provided an additional heating structure for inductor C. This structure includes a conductor loop 50 connected in electrical series with the input lead 44 of the previously described portion of the inductor. Conductor loop 50 includes a parallel conductor 52 positioned adjacent parallel conductor 32 and best shown in FIGS. 4-6. The parallel conductor 52 forms an auxiliary conductor for providing additional heating to surface 10 as workpiece B is rotated by motor 20. The improved inductor includes an additional parallel conductor 54 formed in conductor loop 50. As was the case with conductor 30, conductor 54 is considered to be a single conductor spaced from and adjacent to conductor 30; however, the conductor 54, for electrical purposes includes two separate portions divided by a central gap 56 similar to gap 40 of conductor 30. To complete the electrical circuit of loop 50, there are provided cross-over conductors 60, 62 generally concentric with axis a. Conductor 60 is adjacent cross-over conductor 36, and conductor 62 is adjacent cross-over conductor 34. As best seen in FIG. 1, conductor 60 is an arcuately shaped conductor spaced axially from conductor 36 and spaced from the cylindrical surface of portion 10 substantially the same distance as the cross-over conductor 36. In the flange area of workpiece B, the cross-over conductor 62 is radially spaced from conductor 34 and terminates in lower connecting portions 64, 66 which connect the arcuately shaped cross-over conductor 62 with the lower parallel auxiliary conductors 54, 52, respectively. By using these connecting portions, the auxiliary conductors 52, 54 can be positioned in magnetic coupling relationship with cylindrical portion 10 and below the conductors 30, 32, respectively. In this manner, four elongated parallel conductors are in heating relationship with the body portion 10 as the workpiece is rotated.

To provide alternating current for energizing inductor C, auxiliary conductor 54 at the position adjacent input lead 44 is provided with an input lead 68 connected with the auxiliary conductor 54 by a connecting portion 70 which allows the input lead 68 to be positioned generally in the same plane as the input lead 42 of parallel conductor 30. A source of alternating current, schematically represented as generator 80 includes output leads 82, 84 connected onto leads 42, 68 to create alternating current flow through the inductor C. By providing the arrangement as illustrated in the figures, the current flow within conductors 30, 54, conductors 32, 52, conductors 34, 62, and conductors, 36, 60 are in phase. This phase relationship is indicated by the arrows in FIG. 1. In view of this arrangement, the flux fields created by the primary and auxiliary conductors in all areas of inductors C are additive and do not cancel each other during the induction heating operation. It is appreciated that the flux density about each conductor within inductor C can be reduced and still create heating effect equivalent to the heating caused by increased flux density in prior single shot inductors. This is accomplished because of the increased length of the current path in the inductor. A reduced flux density creates a lesser flexing action during cycling of the inductor. In addition, there are increased number of connections between cross-over and parallel conductors to absorb the flexing action. For these reasons, the life of the inductor is increased by reducing the propensity to create fatigue failure of the inductor. The reduced flux density causes a lesser outward force on the inductor during the heating operation. As a larger area is affected during the heating operation, the efficiency of the heating operation can also be increased.

In accordance with normal practice, L-shaped high permeability flux concentrating elements 90 are provided on cross-over conductors 34, 62 as shown in FIG. 3. In a similar manner, U-shaped flux concentrators 92 can be provided over the cross-over conductors 36, 60. These flux concentrators can be provided along the length of the parallel conductors to increase the heating efficiency of the total installation. The use of these high permeability flux concentrators is well known in the art and does not form a part of the present invention.

Claims

Having thus described our invention, we claim:

1. An improvement in an inductor for inductively heating an elongated cylindrical workpiece having an elongated body portion with a generally cylindrical outer surface as said workpiece is being rotated about a central axis, said inductor including a pair of elongated generally parallel conductors extending along said cylindrical surface and generally parallel to said axis; a first cross-over conductor joining said parallel conductors at one of their ends; a second cross-over conductor joining said parallel conductors at the opposite ends thereof; and, input means for passing an alternating current through said conductors as said workpiece is rotating, said input means including two input leads connected at a gap in one of said parallel conductors, the improvement comprising: said input means further comprising a conductor loop including at least one auxiliary conductor extending along said surface and between a first position adjacent said first cross-over conductor and a second position adjacent said second cross-over conductor, said auxiliary conductor being magnetically coupled to said surface and means for connecting said conductor loop in electrical series with one of said input leads.

2. The improvement as defined in claim 1 wherein said auxiliary conductor is generally parallel to said parallel conductors and adjacent one of said parallel conductors.

3. The improvement as defined in claim 2 including means for causing the current flow in said auxiliary conductor to be in phase with the current flow in said one parallel conductor.

4. The improvement as defined in claim 3 wherein said conductor loop includes a second auxiliary conductor generally parallel to and adjacent to the other of said parallel conductors.

5. The improvement as defined in claim 4 wherein said conductor loop includes a cross-over conductor extending between said auxiliary conductors and generally concentric with said cylindrical outer surface.

6. The improvement as defined in claim 5 wherein said cross-over conductor of said conductor loop is adjacent to said first cross-over conductor and including means for causing the current flow in said cross-over conductor of said connector loop to be in phase with the current flow in said first cross-over conductor.

7. The improvement as defined in claim 6 wherein said cross-over conductor of said conductor loop is spaced axially from said first conductor and spaced from said outer surface a distance generally equal to the spacing of said first cross-over conductor from said surface.

8. The improvement as defined in claim 6 wherein said cross-over conductor of said conductor loop is spaced radially from said first cross-over conductor and generally concentric with said first cross-over conductor.

9. The improvement as defined in claim 1 wherein said conductor loop includes an arcuate conductor extending circumferentially with respect to said outer surface and magnetically coupled to said surface.

10. The improvement as defined in claim 9 wherein said arcuate conductor is adjacent said first cross-over conductor and including means for causing the current flow in said arcuate conductor to be in phase with the current flow in said first cross-over conductor.

11. The improvement as defined in claim 10 wherein said arcuate conductor is spaced axially from said first cross-over conductor and spaced from said outer surface a distance generally equal to the spacing of said first cross-over conductor from said surface.